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The present work is a continuing study on anomalous properties of the ferroelectric nanocomposite from triglycine sulfate (TGS) and oxidized multiwalled carbon nanotubes (OMWCNT). In this study, the nature of frequency response in a region of 102–107 Hz at low temperatures (63–273 K) will be clarified by analyzing structural changes when reducing temperature. It was found that the interaction between TGS and OMWCNT inhibited the switching of SO4- groups, leading to a significant increase in relaxation time, activation energies and coercive fields. Consequently, the domain – wall freezing occurred at higher temperatures than those in pure TGS. [ABSTRACT FROM AUTHOR]

Ferrite samples of composition Cu 0.12 Ni 0.23 Zn 0.65 (Fe 2 O 4) have been prepared by a conventional ceramic process using different sintering temperatures and dwell times. The average particle size is around 25–30 nm and, after sintering, the average grain size increases to 0.2–5 μm and the relative density is between 88 and 95 % of the theoretical density. This paper shows that the mathematical model previously tested on ferrite microparticles with the same composition, is also capable to fit the measured complex magnetic permeability-imaginary part (μ ″) and to explain why this magnetic property decreases when the particle size of the starting powder changes from micro to nano size. The model confirms the dependence of the magnetizing mechanisms (spin rotation and domain-wall motion) on the two microstructural parameters: average grain size (G) and relative density (ϕ) of the sintered body. [Display omitted] [ABSTRACT FROM AUTHOR]

The complex permeability of Cu‐doped nickel‐zinc polycrystalline ferrites is strongly dependent on microstructure, particularly, on relative density (ϕ$\phi $) and average grain size (G$G$). In this study, a mathematical model, able to fit the measured magnetic permeability spectra from 106 to 109 Hz, is proposed and validated for a width range of average grain sizes (3.40–23.15 μm) and relative densities (0.83–0.96). To the authors' knowledge, domain‐wall motion and spin rotation contributions to magnetic permeability have been integrated jointly with the microstructure for the first time in the proposed model, highlighting the relative influence of each magnetizing mechanism and microstructure on the magnetic permeability at different angular frequencies. [ABSTRACT FROM AUTHOR]

The complex permeability of the Cu-doped Ni–Zn polycrystalline ferrites is strongly dependent on microstructure, particularly on relative density (ϕ) and average grain size (G), as it has been shown in a previous study developed at a constant angular frequency (107 Hz). In this study, the previous microstructural model proposed has been extended to an angular frequency range (from 106 to 109 Hz) demonstrating its validity and reliability. In addition, domain-wall motion and spin rotation contributions to magnetic permeability have been individually considered in the mathematical model, highlighting the relative influence of each magnetizing mechanism at different angular frequencies. [ABSTRACT FROM AUTHOR]

One of the critical issues in spintronics‐based technologies is to increase the data storage density. Current strategy is based on shrinking the devices size down to tens of nanometers, or several nanometers, which is reaching its limit. A new proposal is to use multi‐level cells (MLCs) to store more than two bits in each cell. In this work, the multi‐level switching is realized in CoFeB/MgO/CoFeB based nano‐scale single perpendicular magnetic tunnel junctions (p‐MTJs) with three or four stable resistance states. A large range of writing currents for each state is obtained, accompanying with a good repeatability of set‐reset operations between different states. The developed multi‐domain model perfectly matches the experimental results, reflecting the magnetic behaviors during multi‐level switching. Furthermore, current‐driven domain wall (DW) motion is revealed in the circular p‐MTJs, where the DW position can be reversibly manipulated by applied current. To design high‐performance multi‐level p‐MTJs, the parameter diagrams are calculated, suggesting various feasible strategies to improve the multi‐level switching through materials optimization and devices geometry. In summary, the demonstration of multi‐level switching in single p‐MTJ shows the high potential of realizing the new generation of p‐MTJ‐based multi‐level spintronic devices, such as multi‐level memories and spin‐neuron devices. [ABSTRACT FROM AUTHOR]

A new data analysis routine is introduced to reconstruct the change in lattice parameters in individual ferroelastic domains and the role of domain‐wall motion in the piezoelectric effect. Using special electronics for the synchronization of a PILATUS X‐ray area detector with a voltage signal generator, the X‐ray diffraction intensity distribution was measured around seven split Bragg peaks as a function of external electric field. The new data analysis algorithm allows the calculation of 'extrinsic' (related to domain‐wall motion) and 'intrinsic' (related to the change in lattice parameters) contributions to the electric‐field‐induced deformation. Compared with previously existing approaches, the new method benefits from the availability of a three‐dimensional diffraction intensity distribution, which enables the separation of Bragg peaks diffracted from differently oriented domain sets. The new technique is applied to calculate the extrinsic and intrinsic contributions to the piezoelectricity in a single crystal of the ferroelectric PbZr1−xTixO3 (x = 0.35). The root‐mean‐square value of the piezoelectric coefficient was obtained as 112 pC N−1. The contribution of the domain‐wall motion is estimated as 99 pC N−1. The contribution of electric‐field‐induced changes to the lattice parameters averaged over all the domains is 71 pC N−1. The equivalent value corresponding to the change in lattice parameters in individual domains may reach up to 189 pC N−1. [ABSTRACT FROM AUTHOR]

Stress is the crucial factor of ferromagnetic material failure origin. However, the nondestructive test methods to analyze the ferromagnetic material properties’ inhomogeneity on the microscopic scale with stress have not been obtained so far. In this study, magnetic Barkhausen noise (MBN) signals on different silicon steel sheet locations under in situ tensile tests were detected by a high-spatial-resolution magnetic probe. The domain-wall (DW) motion, grain, and grain boundary were detected using a magneto-optical Kerr (MOKE) image. The time characteristic of DW motion and MBN signals on different locations was varied during elastic deformation. Therefore, a time-response histogram is proposed in this work to show different DW motions inside the grain and around the grain boundary under low tensile stress. In order to separate the variation of magnetic properties affected by the grain and grain boundary under low tensile stress corresponding to MBN excitation, time-division was carried out to extract the root-mean-square (RMS), mean, and peak in the optimized time interval. The time-response histogram of MBN evaluated the silicon steel sheet’s inhomogeneous material properties, and provided a theoretical and experimental reference for ferromagnetic material properties under stress.

The neutral-ionic phase transition in TTF-CA was investigated by steady-state and time-resolved infrared spectroscopy. We describe the growth of high-quality single crystals and their characterization. Extended theoretical calculations were performed in order to obtain the band structure, the molecular vibrational modes and the optical spectra along all crystallographic axes. The theoretical results are compared to polarization-dependent infrared reflection experiments. The temperature-dependent optical conductivity is discussed in detail. We study the photo-induced phase transition in the vicinity of thermally-induced neutral-ionic transition. The observed temporal dynamics of the photo-induced states is attributed to the random-walk of neutral-ionic domain walls. We simulate the random-walk annihilation process of domain walls on a one-dimensional chain. [ABSTRACT FROM AUTHOR]

The neutral-ionic phase transition in TTF-CA was investigated by steady-state and time-resolved infrared spectroscopy. We describe the growth of high-quality single crystals and their characterization. Extended theoretical calculations were performed in order to obtain the band structure, the molecular vibrational modes and the optical spectra along all crystallographic axes. The theoretical results are compared to polarization-dependent infrared reflection experiments. The temperature-dependent optical conductivity is discussed in detail. We study the photo-induced phase transition in the vicinity of thermally-induced neutral-ionic transition. The observed temporal dynamics of the photo-induced states is attributed to the random-walk of neutral-ionic domain walls. We simulate the random-walk annihilation process of domain walls on a one-dimensional chain.

Abstract: Domain-wall motion along thin ferromagnetic strips with high perpendicular magnetocrystalline anisotropy driven by spin-polarized currents is theoretically analyzed by means of full micromagnetic simulations and one-dimensional model, both including surface roughness and thermal effects. At finite temperature, the results show a current dependence of the domain wall velocity in good qualitative agreement with available experimental observations, depicting a low-current, low velocity creep regime, and a high-current, linear regime separated by a smeared depinning region. The analysis points out the relevance of both thermal fluctuations and surface roughness on the domain wall dynamics, and confirms that these effects are essential to get a better understanding on the origin, the role and the magnitude of the non-adiabaticity by direct comparison with experiments. [Copyright &y& Elsevier]

Abstract: The mechanism of magnetic field induced magnetic domain-wall (DW) propagation in a nanowire is revealed: A static DW cannot exist in a homogeneous magnetic nanowire when an external magnetic field is applied. Thus, a DW must vary with time under a static magnetic field. A moving DW must dissipate energy due to the Gilbert damping. As a result, the wire has to release its Zeeman energy through the DW propagation along the field direction. The DW propagation speed is proportional to the energy dissipation rate that is determined by the DW structure. The negative differential mobility in the intermediate field is due to the transition from high energy dissipation at low field to low energy dissipation at high field. For the field larger than the so-called Walker breakdown field, DW plane precesses around the wire, leading to the propagation speed oscillation. [Copyright &y& Elsevier]

We investigated the dynamic behavior of 1-3 type magnetostrictive particulate composites as a function of both bias field (5-140 kA/m) and frequency (1-100 kHz). The composites consist of approximately 0.5 volume-fraction Terfenol-D particles embedded and magnetically aligned in a passive epoxy matrix. The measured properties include elastic moduli (E[SUPH,SUB3] and E[SUPB],[SUB3]), dynamic relative permeability (μ[SUBr33]), dynamic strain coefficient (d[SUB33]), magnetomechanical coupling coefficient (k[SUB33]), and the ratio of the dynamic strain coefficient to the dynamic susceptibility (d[SUB33] /χ[SUB33]). We observed the dependence of these properties on bias field and explain it here in terms of domain-wall motion followed by saturation near 40 kA/m. The spectra of μ[SUBr33], d[SUB33], and d[SUB33]/χ[SUB33] indicate that the magnetization process is independent of frequency and that the effect of eddy-current losses is insignificant up to 100 kHz. The observations agree with predictions made by classical eddy-current theory and suggest that the composites can be operated at significantly higher frequencies than monolithic Terfenol-D. [ABSTRACT FROM AUTHOR]

Stress is the crucial factor of ferromagnetic material failure origin. However, the nondestructive test methods to analyze the ferromagnetic material properties' inhomogeneity on the microscopic scale with stress have not been obtained so far. In this study, magnetic Barkhausen noise (MBN) signals on different silicon steel sheet locations under in situ tensile tests were detected by a high-spatial-resolution magnetic probe. The domain-wall (DW) motion, grain, and grain boundary were detected using a magneto-optical Kerr (MOKE) image. The time characteristic of DW motion and MBN signals on different locations was varied during elastic deformation. Therefore, a time-response histogram is proposed in this work to show different DW motions inside the grain and around the grain boundary under low tensile stress. In order to separate the variation of magnetic properties affected by the grain and grain boundary under low tensile stress corresponding to MBN excitation, time-division was carried out to extract the root-mean-square (RMS), mean, and peak in the optimized time interval. The time-response histogram of MBN evaluated the silicon steel sheet's inhomogeneous material properties, and provided a theoretical and experimental reference for ferromagnetic material properties under stress. [ABSTRACT FROM AUTHOR]

Magnetoelectric coupling in multiferroic heterostructures offers a promising platform for electric-field control of magnonic devices based on low-power spin-wave transport. Here, electric-field manipulation of the amplitude and phase of propagating spin waves in a ferromagnetic Fe film on top of a ferroelectric BaTiO 3 substrate is demonstrated experimentally. Electric-field effects in this composite material system are mediated by strain coupling between alternating ferroelectric stripe domains with in-plane and perpendicular polarization and fully correlated magnetic anisotropy domains with differing spin-wave transport properties. The propagation of spin waves across the strain-induced magnetic anisotropy domains of the Fe film is directly imaged and it is shown how reversible electric-field-driven motion of ferroelectric domain walls and pinned anisotropy boundaries turns the spin-wave signal on and off. Furthermore, linear electric-field tuning of the spin-wave phase by altering the width of strain-coupled stripe domains is demonstrated. The results provide a new route toward energy-efficient reconfigurable magnonics., (© 2021 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

A Terfenol-D continuous-fiber composite with a preferred [112] crystallographic orientation was fabricated by embedding 50-vol% [112]-oriented Terfenol-D continuous fibers of 45 mm long and 1 mm wide in an epoxy matrix, and its magnetic and magnetostrictive properties were evaluated as a function of magnetic field. A [112]-oriented short-fiber composite with reduced Terfenol-D fiber lengths of 4 mm and a randomly oriented particulate composite with irregularly shaped Terfenol-D particles of 10–300 μm size, both with 50-vol % Terfenol-D, were also prepared and characterized for comparison with the continuous-fiber composite and monolithic Terfenol-D. The continuous-fiber composite demonstrated the largest magnetostrictive response with the highest saturation magnetostriction (λs) of 1265 ppm. This λs not only is 23% and 92% larger than the short-fiber and particulate composites, respectively, but also exceeds the monolithic Terfenol-D by 14%. The higher λs compared to the monolithic Terfenol-D, short-fiber composite, and particulate composite mainly originates from the residual compressive stresses developed in the continuous fibers during epoxy cure, a higher fiber aspect ratio for greater stress transfer from the fibers to the matrix, and texturing of the fibers along the highly magnetostrictive [112] crystallographic axis, respectively. [ABSTRACT FROM AUTHOR]

Magnetic reversal behaviors of Au (60 nm)-FePt (x nm) thin films with various x values are investigated. A high temperature heat treatment at 800 °C was applied to obtain an isolated microstructure with L10 FePt particles embedded in a face-centered cubic gold matrix through interfacial diffusion. The coercivity of the thin films was increased from 13.6 kOe to a maximum value of 30.0 kOe as the thickness of the FePt layer was decreased from 200 to 10 nm. From the dc demagnetization and isothermal remanence magnetization measurements, we found that the bilayer sample with x = 10 exhibits larger reversible magnetization. The coercive mechanism was found to be controlled by the magnetization rotation of the isolated FePt particles. As x is increased, the reversal behavior is changed into a domain-wall motion mode gradually. The magnetic force microscopy investigations further confirm the change of mechanism. The domain-wall motion appears to result from the formation of large multidomain grains. Considering the relation of reversal behavior and the coercivity, we thus conclude that the removal of domain walls is beneficial for hard magnetic performance. [ABSTRACT FROM AUTHOR]

The dynamic magnetoelastic properties of a [1121-oriented magnetostrictive composite comprising 0.49 volume fraction of needle- shaped, [112]-oriented Terfenol-D particles and Spurr epoxy were investigated as a function of magnetic bias field. These properties included elastic moduli (E3H and E3B), dynamic strain coefficient (d33), and magnetoelastic coupling coefficient (k33). A randomly oriented composite with 0.51 volume fraction of irregular-shaped, hall-milled Terfenol-D particles was also prepared and characterized for comparison. It was found that the [112] preferential particulate orientation increases non-180° domain-wall motion in the [112]. oriented composite, resulting in maximum negative-ΔE, d33, and k33 values of about 10%, 5.5 nm/A, and 0.34, respectively. These are the largest property values reported as yet for magnetostrictive particulate composites, being up to 67% larger than the randomly oriented composite and approach to 65% of the monolithic Terfenol-D. [ABSTRACT FROM AUTHOR]

Spin-orbit torque (SOT) magnetic random access memory is envisioned as an emerging nonvolatile memory due to its ultrahigh speed and low power consumption. The field-free switching scheme in SOT devices is of great interest to both academia and industry. Here, we propose a novel field-free deterministic magnetization switching scheme in a regular magnetic tunnel junction by using two currents sequentially passing interlaced paths, with less requirements of the manufacturing process or additional physical effects. The switching is bipolar since the final magnetization state depends on the combination of current paths. The functionality and robustness of the proposed scheme are validated through both macrospin and micromagnetic simulation. The influences of field-like torque and the Dzyaloshinskii-Moriya interaction effect are further researched. Our proposed scheme shows good scalability and is expected to realize novel digital logic and even computing-in-memory platforms.

The expansion of magnetic domains in thin films with perpendicular anisotropy is investigated. To determine the domain-wall-velocity as a function of the applied magnetic field a selfconsistent magnetic-viscosity approach is used. The main predictions of the theory are a linear behaviour in the moderately strong fields, a quasi-exponential behaviour for fields close to the propagation field, and a negative velocity for very small and negative fields. The predictions of the theory are compatible with domain-wall investigations on Au/Co/Au sandwiches. [ABSTRACT FROM PUBLISHER]